fix: possible nil table on useStamina function (#1002)

In some scenario where the player is no longer online, but the event is still running, it will give a nil value error when trying to access the table with the player ID, generating the "nil value" error.

data/events/scripts/player.lua

@@ -614,7 +614,7 @@ local function useStamina(player)
 	end
 
 	local playerId = player:getId()
-	if not playerId then
+	if not playerId or not nextUseStaminaTime[playerId] then
 		return false
 	end